1. Field of the Invention
The present invention relates to a gas turbine, in particular in a power plant. The invention also relates to an associated method of cooling the gas turbine.
2. Brief Description of the Related Art
A large portion of the requisite electrical energy is generated in power plants by means of steam and/or gas turbines. The efficiency of these plants is crucially determined by the inlet temperature of the working medium (gas or steam). If higher efficiencies are to be realized, higher temperatures must be adopted. Due to these temperature increases, however, the limit of the material stress is reached very quickly. Intensified cooling of the steam and/or gas turbine is therefore required in order to increase the efficiency. The conventional cooling medium of the hot-gas-carrying components in a gas turbine is air, extracted from the final or intermediate stage of the compressor. Critical locations in this case are the combustion chamber lining, the first vane row, the first blade row, the turbine rotor and the rear compressor section. In general, however, the cooling of steam or gas turbines by means of steam is also known (DE 3003347). On account of its higher thermal capacity and its lower viscosity, steam is in principle a better cooling medium than air. In addition, steam, instead of cooling air, reduces the specific compressor output due to the omission of the pressure losses of the cooling air and reduces the NOx emissions due to a lower combustion chamber temperature at the same turbine inlet temperature.
The steam cooling may be designed as an open or closed system. In an open system (e.g. film cooling of the blades), the steam, once it has fulfilled its cooling task, is admixed with the working gas and thereby acts on the gas turbine in such a way as to increase the output and efficiency.